By the year 1070 the conquest of England by William I was complete, and all the available sequestrated lands had been divided among his followers. But the land hunger of the barons was unappeased; and in order that he might have time to consolidate and to organize his new kingdom, William directed their attention to Wales. That country possessed three obvious gates by which invading armies might enter. The first was Chester, which William himself had visited, and from which the great mountains of Gwynedd could be clearly discerned. The second was Shrewsbury, from which a broad and fertile valley stretched right into the heart of Powys. The third was Hereford, the natural starting point for the conquest of Deheubarth. At each of these points William stationed one of his barons—at Chester the rapacious Hugh the Wolf, at Shrewsbury the able Roger of Montgomery, at Hereford William Fitz Osbern. Using these three towns, at each of which a strong castle was erected, as bases of operations, the earls, in the course of the next fifty years, advanced step by step into the country. Their object was to possess themselves of all the level and fertile land; and their method of conquest was the castle. Opposition to them was always fierce, but seldom united or well advised. The three original barons were soon joined by others; and ere long chains of fortresses stretched out from Shrewsbury, Chester, Hereford, Gloucester, and Cardiff. The English border was thereby studded with them; and so was the whole of South Wales from Gloucester and Hereford to Pembroke and Aberystwyth. They brought with them traders, architects, and craftsmen; and a numerous colony of Flemings made Pembrokeshire their home. At the end of this period of advance it was recognized that to the Normans belonged the Marches, the fertile plains, and the eastern and southern slopes of the mountains; while the rest—a land of dizzy peaks, narrow valleys, and bleak moorland—remained in the hands of the Welsh people.

The records of these years of conquest are interesting and sometimes thrilling, but neither edifying nor instructive. They are replete with martial exploits and deeds of daring. Battles are fought, and castles are stormed and burned with wearisome monotony. On both sides there was cruelty and treachery in abundance. A few names stand out as deserving of remembrance. The men who did most to stem the on-coming tide of Norman invasion were Griffith ap Conan, and Griffith ap Rees, both of whom died in the year 1137. The former ruled in Gwynedd, and the latter in Deheubarth; and to a far greater degree than any other Welsh princes of the period they perceived how absolutely essential unity was if Wales was to be saved from becoming a Norman fief. By this time the Welsh had learnt much of the Normans' military art. They fought clad, like their foes, in complete armour; and they knew how to build, how to defend, and how to attack stone castles. Thus the disparity in equipment, which had at first made Welsh armies an easy prey to much smaller bodies of Normans, was disappearing. In 1136, the year after the death of Henry I, a great pitched battle was fought at Cardigan between Griffith ap Rees and a league of Norman barons formed in order to crush him; and in this battle the Welsh were victorious. The Normans retreated, and were obliged to abandon much of the land and several of the castles which they had previously held. This is the high-water mark of the power of the Norman barons as distinct from that of the Norman kings.

An even greater ruler then ascended the throne of Gwynedd, the famous Owen Gwynedd, fine soldier, far-sighted statesman, friend of poets, and patron of monks. He perceived, dimly at least, the utter hopelessness of the struggle, which had now begun in earnest, against incorporation in the English kingdom, unless complete national unity could at once be achieved. Henry II now sat on the throne of England; for the times of Stephen and Matilda, so helpful to the enemies of England, were over. Owen persuaded most of the Welsh chieftains to acknowledge his supremacy; and he made an alliance with the princely house of Dinevor, the rulers of South Wales. But for the utter selfishness and the treachery of his brother there is no knowing but that something like a united Wales might have emerged before the close of Owen's reign. Never was unity so sorely needed; for one of the first enterprises upon which Henry II embarked, when he had made his throne secure, was the subjugation of Wales. But Henry's first venture was unsuccessful. Starting from Chester, he penetrated as far as Rhuddlan; but was there confronted with the great mountain mass of Snowdonia, stretching right into the sea at the Penmaenmawr. He occupied Anglesey, however; but so fierce was the opposition with which he was met that he deemed it wise to come to terms with Owen, and to withdraw.

In 1157 Henry came a second time, but with no better results. Twelve years later he led his armies into Wales for the third time, on this occasion starting from Oswestry, and crossing the mountains into the upper valley of the Dee. At Corwen Owen's army was drawn up in readiness, an army fairly representative of the whole of Wales. Before the English could reach him, however, the wind and the rain had done their work upon the invaders. Baggage was washed away, and to obtain adequate supplies became an impossibility. Angry and disappointed, Henry was obliged hurriedly to retreat. This was the crowning triumph of Owen Gwynedd's life. He had successfully withstood one of the very greatest of English kings. In the November of the same year he died, and was buried in Bangor cathedral.

In the years which immediately followed the death of Owen the dominating figure in Welsh politics was Rees ap Griffith, prince of Deheubarth, the "Lord Rees" as he was generally and familiarly styled. He inherited Owen's policy of unity and consolidation; but this time the work was to proceed from Cardigan, and not from the mountains of the North. The task of repelling the advance of the Normans was now less formidable than it had ever been; for the conquest of Ireland had begun, and the more turbulent and adventurous spirits were finding there an outlet for their energies in just the same way as their grandfathers had done in Wales. When king Henry II passed through Wales on his way to Ireland, he was met by the Lord Rees, and an amicable understanding was arrived at between them. In 1174 Rees was able to give proof of his friendship by assisting Henry to crush a revolt of his barons. Slowly but steadily Rees extended his sway over all the princes and barons of the South; and even over Merioneth beyond the Dovey, the natural boundary between his dominions and those of the princes of Gwynedd. Not only was Rees a great warrior, and an able statesman; he was also a munificent and discriminating patron of culture. An Eisteddfod which he held at Cardigan in 1176 has become famous. There poets and musicians from every part of Wales competed; and so just were the awards that the prize for music was won by the South, and that for poetry by the North.

The closing decade of the twelfth century saw the accession to the throne of Gwynedd of the ablest statesman in the whole history of mediæval Wales. This was Llewelyn, known to English and Welsh historians alike as Llewelyn the Great. It was no novel spectacle to see one of the Welsh thrones occupied by a fine soldier; and great as Llewelyn undoubtedly was in that respect, he was no greater than some of his predecessors and some of his successors. Where he outshines all competitors is in his clear reading of the signs of the times, in his understanding of the politics of England as well as Wales, and in his firm grasp of a policy which was no fantastic dream but a theory possible of attainment. His long reign of forty-six years (1194-1240) divides itself naturally into some half-dozen periods. In the first period (1194-1201) Llewelyn is fully absorbed in the task of making himself secure on the throne of Gwynedd. His difficulty was with the members of his own family, and with Prince Gwenwynwyn of Powys. The emergence of Gwynedd from the obscurity which had recently overtaken it was also beheld with jealous eyes by the princes of the South. But from all these difficulties Llewelyn soon emerged triumphant. In the course of the struggle he had, however, learnt one thing, and that was that the only hope for Wales lay in submission to the king of England, a submission which would involve only an acknowledgment of overlordship, without the abandonment of one single title of substantial independence. He perceived clearly that to fight for the shadow would probably lead to the loss of the substance; especially as it had now been proved beyond all possibility of doubt that the Welsh princes never would submit permanently and peacefully to one of their own order.

The second period in Llewelyn's reign opens with his marriage to Joan, daughter of King John. The marriage alliance carried with it a political alliance as well. Llewelyn used the brief breathing space which this alliance brought him to the best possible advantage. He made his position in Gwynedd secure, overran Powys, and carried his victorious army as far south as Aberystwyth. There he met the southern princes, and agreed to divide Cardigan with them. Then turning northwards he marched against Ranulf, Earl of Chester, whose castles of Deganwy, Rhuddlan, Holywell, and Mold he captured.

In the meantime John had been viewing the victorious career of his son-in-law with surprise and displeasure. A strong and united Wales was a thing which no king of England could tolerate. In the third period of his reign, therefore, between 1212 and 1215, we find John and Llewelyn in opposition to one another. Twice in the course of one summer did John invade North Wales, penetrating on the second occasion as far as Bangor, where, characteristically enough, he burned the Cathedral, and held the Bishop to ransom. So hard pressed was Llewelyn that he was obliged to send Joan to make full submission to her father on his behalf. But the tide soon turned. The other Welsh chieftains were greatly alarmed at John's manifest intention to dispossess them; and placing themselves under Llewelyn they begged him to lead them. John had also quarrelled with Rome; and the great Innocent III, who then held the Papacy, absolved Llewelyn and the other Welsh princes from their allegiance to the English king. Events in England were also most propitious; for John had by now come into serious conflict with his own nobility, and was soon to be compelled to concede all their demands by the Charter. With the English barons Llewelyn made an alliance; and Magna Carta, when it was eventually signed, contained clauses dealing exclusively with Wales. One of these clauses consisted of a promise that all Welshmen dispossessed of their lands or liberty should recover them. Another declared that all disputes were to be decided in England by English law, in the Marches by March law, and in Wales by Welsh law.

In the year 1213 John had convened a council, in which some have seen the germ out of which grew the future English Parliament. The same idea seems to have found place in the mind of Llewelyn; for on two occasions he summoned together all the princes of Wales, and all the wise men. So far as we know there was no process of election, and certainly no trace of the principle of representation; nevertheless this council was a distinct advance politically upon anything that had been seen in Wales before. The princes were to act as judges, and all questions of policy were to be debated by them with the assistance of the wise men. The first of these councils assembled at Aberdovey, a convenient meeting-place for Gwynedd, Powys, and the South. The decrees of the council were to be upheld by force; and when Gwenwynwyn of Powys soon after refused to obey, he was instantly crushed and deprived of his lands.